Deployment of Contents Protection Scheme using Digital Signature
Daichi Tanaka
1
, Keiichi Iwamura
1
, Masaki Inamura
2
and Kitahiro Kaneda
3
1
Tokyo University of Science, 6-3-1 Niijuku, Katsushika-ku, Tokyo, 125-8585, Japan
2
Tokyo Denki University, Ishizaka, Hatoyama-machi, Hikigun, Saitama, 350-0394, Japan
3
Osaka Prefecture University, 1-1 Gakuencho, Naka-ku, Sakai, Osaka, 599-8531, Japan
Keywords: Copyright Protection, Edit Control, Digital Signature, BLS Signature, Aggregate Signature, Mounting.
Abstract: With the recent progress in social media and Internet technology, it is easy for consumers to edit contents
uploaded on the network and create new contents. In this situation, copyright protection related to the
secondary use of uploaded content is important. In our previous works, three schemes were proposed for
controlling the secondary use of content according to the author's intentions by using digital signatures. Using
these schemes, an author can control the changes, deletions, additions, and diversions in each portion of
his/her contents, as well as the composition of the contents. The objective of this study was to verify the
practicality of this technology by mounting it. Thus, we applied this technology to contents created using
"MikuMikuDance," a contents editing tool for 3D CG movies, and mounted a contents protection system. We
show the manner in which this system was mounted, and describe the evaluation of the processing speed in a
simulation environment.
1 INTRODUCTION
In conventional mainstream content distribution
services, the service, which is a specific addresser,
such as a television station or a publishing company,
provides contents to consumers. Recently, however,
an environment where consumers can create content
has become available, and they can publish their
content easily on the Internet. Platforms for the
circulation of content are called consumer generation
media (CGM) services. As Web services that provide
CGM services, YouTube, Niko Niko, etc. are well
known. Within these CGM services, contents
circulation, where not only are new contents created,
but also the contents that other authors have created
are edited and published as new contents, prospers.
In this situation, viewing control and copy control
technologies, which are the current mainstreaming
copyright protection technologies, are not suitable for
CGM contents, because they constrain the circulation
and editing of contents. In content circulation, new
copyright protection technologies, such as rights
succession, where the original author’s rights are
inherited, and edit control, which allows an edit of
contents only in alignment with the author’s
intentions, even if the contents are used secondarily,
are required.
In our previous works, three copyright protection
schemes that realize rights succession and edit control
by using digital signatures were proposed. Using
these schemes, a contents protection system that can
control the secondary use of contents to meet the
author's intentions was realized. It allows an author to
control changes, deletions, additions, and diversions
in each portion of his/her contents, and to control also
the composition of the contents themselves using
signatures.
This study was aimed at verifying the validity of
this contents protection system by mounting it. We
applied it to contents created by "MikuMikuDance,"
which is a content edit tooling for 3D CG movies. The
mounted program covers only the change function
using a Boneh-Lynn-Shacham (BLS) signature,
which constitutes the foundations of the system. We
demonstrate signature creation and signature
verification for changing the contents created by
"MikuMikuDance" in an actual content creation
environment. We show how this function is mounted,
and present an evaluation of the processing speed in
a simulation environment.
In this paper, Section 2 presents the principles of
the edit control schemes presented in our previous
works and the basic knowledge required to use them.
Section 3 describes "MikuMikuDance," which has
been mounted, and Section 4 shows the restrictions
130
Tanaka, D., Iwamura, K., Inamura, M. and Kaneda, K.
Deployment of Contents Protection Scheme using Digital Signature.
DOI: 10.5220/0006472501300137
In Proceedings of the 14th International Joint Conference on e-Business and Telecommunications (ICETE 2017) - Volume 2: ICE-B, pages 130-137
ISBN: 978-989-758-257-8
Copyright © 2017 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
on mounting and an algorithm mounted in the
program, and explains the application of the
algorithm to the contents in "MikuMikuDance."
Section 5 describes the simulation environment and
the evaluation results, and in Section 6 a summary is
presented.
2 RELATED WORK
We have proposed three schemes which provide
rights succession control and edit control. First, a
fusion of rights succession and edit control is
realized(Masaki, 2012); however, the scheme
addresses the edit of only one content. Next, rights
succession and edit control involving two or more
contents is realized using a BLS signature (Katsuma,
2015); however, this paper proposed only scheme
without how to realize it with contents. latest,
correspondence to an ID based signature is
realized(Tatsuya F. 2016), so that the collection and
verification of a public key certificate is unnecessary.
In this study, we mounted the change function
proposed in second study using the BLS signature for
fundamental functional verification. Therefore, in the
following we describe the BLS signature and the
outline of the scheme proposed in Katsuma’s study.
2.1 Aggregate Signature Scheme based
on Boneh-Lynn-Shacham Signature
Boneh, Lynn, and Shacham proposed an aggregate
signature scheme (Boneh, 2003) based on the Boneh-
Lynn-Shacham (BLS) signature scheme (Boneh,
2001) using an operation on an elliptic curve and
pairing. This scheme aggregates two or more
different signatures for every message into one
signature, and makes the signature size a steady
length that is not dependent on the number of signers.
We denote by
a set of signers
in a group who participate in generating an aggregate
signature, and by
a set of symbols of
these signers. Then, the construction of the aggregate
signature is as follows.
[Key Generation]
where is a generator of
.
is the value of
.
The key generation center calculates
(1)
where
represents a private key of
and
a
public key of
.
[Signing]
We denote by
a one-way hash
function.
is a message of a signer
. Then, signer
calculates
(2)
(3)
as his/her signature corresponding to
. After the
signers have set their signatures, all the signatures are
collected and calculated
(4)
as an aggregate signature.
[Verification]
The verifier collects
and the
verification keys
, and then, calculates
from all
and determines whether
(5)
is realized using pairing. If the aggregate signature is
created correctly, the above equation is realized.
2.2 Concept of Edit Control using
Signature
2.2.1 Edit Control
In the scheme presented in Katsuma’s study
(Katsuma, 2015), an author divides his/her content
into partial contents, sets the signatures of each partial
content, and aggregates these signatures to one
signature for the content. Hereafter, we call the
signature of the partial content the edit control
signature. If an author permits editing of the partial
content, he/she exhibits the edit control signature.
When an editor changes the partial content, the edit
control signature is deleted from the aggregate
signature and a new signature of the editor’s partial
content is added to the aggregate signature. If the
author does not permit editing of the partial contents,
he/she keeps the edit control signature secret. In this
case, an editor cannot edit the partial contents because
he/she cannot change the edit control signature in the
aggregate signature.
In this scheme, as the edit control signature to
control the changes, deletions, and additions of partial
content two types of signature are set: change control
and deletion control. Addition control is realized by
change control, as the addition of content is realized
by changing empty data to real data, as discussed later.
Deletion refers to changing real data to empty data.
However, deletion control needs to be independent of
change control. For example, the control of a fixed
form, such as a four-frame cartoon, allows each frame
to be changed; however, in order to prevent breaks in
the fixed form the control does not allow the deletion
Deployment of Contents Protection Scheme using Digital Signature
131
of frames. More specifically, in a movie, credit title
deletion is allowed, but a change is not.
This scheme enables not only an edit in one of the
contents, such as a change, addition or deletion of
partial contents, but also an edit involving two or
more contents, using the diversion control signature
and composition control signature. The diversion
control signature controls whether a partial content
can be used in other contents, and the composition
control signature controls whether two contents can
be compounded. However, in the case of this
mounting, since an edit involving more than one
content is not addressed, the explanation is omitted.
2.2.2 Entities
In this scheme(Katsuma, 2015) the i-th author is
introduced without using the word "editor" and two
entities called the i-th author and a verifier are defined
as follows.
The i-th author
The i-th author is involved in a work, and can set up
edit control signatures for the partial contents and
update the aggregate signatures. For simplicity, we
express the work using a tree structure, as shown in
figure 1. In this scheme, each author who is in the
deepest portion of the tree is called a 1st author, and
an author who is in a portion of the tree route is called
the n-th author when the tree height is n-1. Therefore,
i is defined as the author’s position in the work. The
i-th author can set the edit control signature for the
partial contents that he/she has produced or edited
only when an edit is permitted by the edit control
signatures defined by the (i-1)-th authors. In figure 1,
A11 to A16 are the primary contents created by two
or more 1st authors; the 2nd authors created the
secondary contents A21 and A22 using the primary
contents of the 1st authors. Finally, the 3rd author
produces the final content A31. Here, the 2nd authors
can edit partial contents according to the setting of the
edit control signature by each 1st author, and the 3rd
author follows the setting of the entire edit control
signature by the 1st and 2nd authors.
Figure 1: Examples of entities in the tree structure of a work.
Verifier
The verifier verifies whether a content has a valid
signature. If this function is available in a program
that reproduces contents, we can construct a system
such that the content cannot be reproduced if it does
not have a valid signature.
2.2.3 Contents and Partial Contents
In this scheme, the partial contents consist of two
types of data: empty and real. The empty data are
placed in the portion that is to be added or deleted,
and the real data constitute the displayed contents.
The empty data are treated as control data for
controlling addition and deletion, and the control data
are not included in the displayed contents.
An author produces one or more partial contents
and makes them available to the public in the
following form as a content. A content comprises the
start data, one or more partial contents, and the last
data. The start data and the last data are the control
data. Each data item is identified by an identifier.
This scheme detects edits that are contrary to an
author's intention, but does not prevent just contents
from turning into unjust contents by means of a
processing violation, such as an overwrite or a change
in the parameters. Since only the just copied contents
are edited, the original contents are not affected by a
processing violation. Therefore, even if an attacker
does violate processing, he/she gains no advantage
only because the edited contents become unjust
contents.
2.2.4 Algorithm
In this section, we explain the specific algorithm
presented by other work (Katsuma, 2015). However,
we omit the explanation of the processing procedures
other than changes, because of the page limit. In this
algorithm, it is assumed that the binding between the
signers and the verification keys is guaranteed by a
certification authority, and the information that is
being prepared is not obtained by a third party.
[Key Generation]
ID
ij
is the author ID defined according to the location
of a work. For example, ID
11
is the author of contents
A11 in Figure 1. Each ID
ij
has a secret key
,
and exhibits the public key
. All of the
signing keys are different.
[Signing]
The author always performs this signature generation
process before publishing the original content.
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1. Author ID
ij
determines the control permissions
for changes for each partial content. Author ID
ij
determines the content ID of his/her created contents
as IC
ij
.
2. Author ID
ij
sets the start data as A
ij0
* and the last
data as A
ijm+1
* for m partial contents. Here, d is the
message of the control data. Then, author ID
ij
generates the start signature
and the last signature
. The constant varies according to the edit, but
here only the value over change is used.
(6)
(7)
(8)
(9)
3. Author ID
ij
creates data A
ijk
* for the message of
each partial content A
ijk
:
(10)
4. Author ID
ij
generates a hash value:
(11)
5. Author ID
ij
generates an edit control signature
for changes for every the partial content:
(12)
6. Author ID
ij
creates an aggregate signature:
(13)
7. Author ID
ij
keeps
secret, if he/she does not
allow changing.
[Updating Signatures for Editing]
Let us consider the case where Author ID
ab
changes
the partial content A
ijk
in the content A
ij
, which is
created by Author ID
ij
, to A
abk
, which he/she created.
8. Author ID
ab
confirms whether editing of
contents A
ij
is allowed using the signature
verification. If editing of contents A
ij
is not allowed,
then the edit is stopped.
9. When a change is permitted, author ID
ab
can
substitute A
ijk
with A
abk
, and decides the edit
permission of A
abk
.
10. Author ID
ab
generates the data A
abk
* and the hash
value for the substituted partial contents.
(14)
(15)
11. Author ID
ab
generates a new edit control
signature
of A
abk
, as in Step 5 during the signing
process by using his/her signing key.
12. Author ID
ab
updates the aggregate signature as
follows. Here, the author cannot update of the
aggregate signature, if
is not disclosed.
(16)
[Verification]
The verification of the content is performed by the
reproduction machine before viewing or the
secondary use of the content by the viewer. Here, the
entity that performs the signature verification of the
content is called the verifier. The verifier performs the
following processing.
First, the verifier generates the hash value of each
partial content for each edit. The verifier prepares the
key of the authors and verifies the following
equations. If the results of the examinations are
correct, the content is accepted as valid.
(17)
3 “MikuMikuDance” AND ITS
CONTENTS
3.1 About “Miku Miku Dance”
“MikuMikuDance” is a 3D video production tool
released by Yu Higuchi as a free program.
“MikuMikuDance” was first used as a tool for
creating dance movies featuring “Hatsune Miku.”
The most recent version allows the editing of other
3D models and many types of 3D movies. Therefore,
it is very easy to start to produce a 3D CG video using
“MikuMikuDance,” since a considerable amount of
material is available on the Internet. Figure 2 shows
the creation of 3D CG movies using
“MikuMikuDance.”
Figure 2: Creating contents in “MikuMikuDance”.
Deployment of Contents Protection Scheme using Digital Signature
133
3.2 Composition of Contents
In figure 2, each girl is a 3D model. A 3D CG movie
comprises a set of 3D models, music, and so on. First,
“MikuMikuDance” loads 3D models, music files, and
voice files as material of 3DCG videos and creates a
3DCG movie by editing them. The correspondence
with the contents of "MikuMikuDance," shown in
Table 1, was defined in Katsuma’s paper (Katsuma,
2015) and the signature creation tool and signature
verification program were created for them.
Table 1: Relationships in our implementation.
Define in
Katsuma’s study
Define in
"MikuMikuDance"
A set of contents
3DCG movie
A content
3D model
Partial contents
Bone(shape)
Morph(face emotion)
Motion(physical motion)
In "MikuMikuDance," the operation of each part
of a 3D model is not defined frame by frame.
"MikuMikuDance" controls each partial content of a
3D model through operation directions such as "A
specific part is moved at a specific time to a specific
position." For example, “arm is at upper left in Frame
5, lower left in Frame 15, and returns to this point in
Frame 30.” The motion in the meantime is added by
"MikuMikudance." The contents created by
"MikuMikuDance" specify the appearance, motion,
etc. using a pmm file. Figures 3 and 4 illustrate this.
The description of one motion is defined as one
partial content, and a set of descriptions comprising
the whole motion of a 3D model is defined as one
content. Finally, two or more contents are
compounded and saved as one 3D CG movie.
Figure 3: Construction in .pmm files.
Figure 4: Direction of 3D models.
4 RESTRICTION IN
IMPLEMENTATION
We aimed at mounting all the functions presented in
our past work. However, it is difficult to mount all of
them in time and functionally. For example, empty
data, which are not displayed although they exist to
control addition and deletion, cannot be prepared in
“MikuMikuDance.” Therefore, addition and deletion
cannot be realized. However, the aim of this
mounting was to demonstrate the new edit control,
and to show that the processing speed for signature
creation and verification is practical. Therefore, we
focused on the change processing procedure
described in 2.2.4, which is a basic function, and
evaluated the performance of the system.
In addition, when edits that are not allowed are
detected, the program displays a processing violation
detection message immediately. However, since this
program is not unified with “MikuMikuDance,” the
actual processing of “MikuMikuDance” cannot be
stopped.
Below, we show the mounted algorithm and an
example of processing the signature creation and
verification using the mounted program.
4.1 Mounted Algorithm
The key generation described in 2.2.4 is performed a
priori and set up. The process shown in figure 5(a)
includes the pretreatment before the signature process
described in 2.2.4. The pretreatment consists of the
extraction of each partial content. The pmm data of
original content consist of various types of data, one
of which constitutes information about the 3D model,
for example, “shape,” “move,” and “emotion.”
Another type of data consists of temporary
information used for editing. The data used for the
signature are only the bone, morph, and motion of the
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134
3D model in Table 1, and they are extracted as the
target file. The signing described in 2.2.4 is
performed for each partial content in the target file.
The process shown in figure 5(b) is the signature
update process after an edit. This program saves the
hash value of the partial content before the edit. After
an editor edits a content, a hash value is created for
the edited partial content and the program compares
the two hash values. If there are some differences, a
change is detected. After this detection, the updating
signature described in 2.2.4 is performed and the
signatures are updated.
Figure 5: Overview of copyright protect algorithm.
4.2 Concrete Simulation Sample
4.2.1 Extract Partial Contents
Our program runs with the command lines shown in
figure 6; the created target file described in 4.1 is
shown in figure 7. Figure 6 shows the title of the
program and the completion date of the latest version.
Then, the following steps are executed: 1. signing, 2.
extraction of edited parts, 3. signature verification, 4.
saving of the signature, 5. verification of signatures,
0. end; the input of a processing number.
Figure 6: Running copyright protection program.
Figure 7: Excel view of generated target file.
In figure 7, the Japanese strings represent the
names of the parts of the 3D model. The second
column indicates whether the signature can be
changed, where 1 means enable and 0 means disable.
The numbers 1, 2, 3… are the serial numbers of the
partial contents. The hexadecimal strings are the hash
values of the partial contents.
4.2.2 Create Signatures
Using the target file, the digital signatures as edit
control signatures are calculated, as described in 4.1.
The signatures are also stored in an Excel signature
file. In this program, all the signatures are managed
in an Excel file, although each signature is attached to
each partial content in the scheme.
Figure 8: Excel view of generated signature file.
Figure 9: Signature update program.
Deployment of Contents Protection Scheme using Digital Signature
135
4.2.3 Verification of Signature
Figure 9 shows the screen for verifying whether the
updated signature and the signature for the edited
contents are in agreement.
5 SIMULATION METHOD AND
EVALUATION
5.1 Simulation Environment
The simulation was executed in a computer running
the Oracle Virtual Box and a virtual OS. Table 2
shows the details of the simulation environment. The
simulation compiled the program written in C
language using GCC (version 5.4.0), and ran it on the
Ubuntu terminal. For each operation described in
2.2.4, TEPLA was used for the pairing operation,
elliptic curve calculation, and operation in the finite
field on the computer. TEPLA was updated to the
latest version on 20 Dec. 2015.
Table 2: System environment in simulation.
Main machine
Details
OS
Windows 7 Home Premium
SP1 64bit
CPU
Intel® Core™
i5-2450 M CPU 2.5 GHz
RAM
8.00 GB
Virtual
machine
Oracle Virtual Box
Version
Version 5.0.26
Virtual OS
Ubuntu16.04 LTS
CPU
Same as main machine
RAM
3.00 GB
This environment is limited as compared with the
most recently developed computers. However, if this
simulation was executed at a speed permissible in
practice, it would show that the content protection
scheme is effective and practical.
5.2 Outline of Simulation
To verify the operation of the mounted program and
evaluate it, we changed the number of the 3D models
and the number of partial contents comprising each
model, measured the time spent on processing two or
more times, and recorded the average time.
Version 9.26 of “MikuMikuDance” was used.
The number of 3D models and of their partial contents
of the MikuMikuDance standard attachment used in
this simulation are shown in Table 3.
Table 3: Number of target 3D model(s) and partial contents.
Models
Partial contents
1
4052
2
6999
3
10070
4
12739
5
15800
5.3 Simulation Results
5.3.1 Generate Signature
We measured the time taken by the signature
generation process five times for every number of
models and partial contents. The total required time
and the time required per 1 partial content are shown
in Table 4.
The signature targets include the aggregate
signatures.
Table 4: Time spent on signature generation.
Models
Number of
signature
targets
Required
time (ms)
Time per
1 target
(ms)
1
4052
2951.01
0.7283
2
6999
5683.37
0.8120
3
10070
7583.61
0.7531
4
12739
9912.55
0.7781
5
15800
11677.51
0.7391
As seen in Table 4, the processing speed per one
target is satisfactory and practical: 0.7 ms–0.8 ms, and
all the throughputs increase in proportion to the total
time for the targets. In general, a movie of about 25
sec comprising one model needs approximately 3000
signatures. In this case, the signature generation time
of one movie is about 3 sec. If the signature
generation process is performed whenever some
contents are created, a signature generation time of
several seconds can be considered satisfactory and
practical.
5.3.2 Signature Verification
We measured the time required for signature
verification 10 times for every number of models and
partial contents. The total required time and the time
required per 1 partial content are shown in Table 5.
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The signature targets include the aggregate
signatures.
Table 5: Time spent on signature verification.
Models
Number of
signature
targets
Required
time (ms)
Time per
1 target
(ms)
1
4052
2150.18
0.5306
2
6999
4174.38
0.5964
3
10070
5967.22
0.5926
4
12739
7661.56
0.6014
5
15800
11336.42
0.7175
When first verifying the signatures of a content,
all the signatures for all the content must be verified,
and the time varies according to the number of
signatures. However, during editing the signature
verification process is performed only for the edited
portion and can be performed for each edit in several
seconds. This can also be considered satisfactory and
practical.
6 SUMMARY
In this study, we developed a program to generate and
verify signatures and mounted a contents protection
system for“MikuMikuDance,” which is a content
editing tool for 3D CG movies. Through this
mounting, we showed that the scheme can be applied
not only in theory but also in an actual application,
and that the processing speed achieved is satisfactory
and practical.
In future work, we will extend the functions to
handle addition, deletion, and diversion of partial
contents and the composition of contents, which
includes all the functions in the scheme presented in
Katsuma’s work (Katsuma, 2015). In addition, we
will also examine mounting using the ID-based
signature (Tatsuya, 2016) and the fusion of edit
control and rights succession control(Masaki, 2012)
to realize many functions. Improvement in the speed
of processing and the system’s application to various
applications should also be considered.
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Youtube, https://www.youtube.com/
Niko Niko Douga, www.nicovideo.jp/
Yu H. ,VPVP http://www.geocities.jp/higuchuu4/
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University of Tsukuba, "TEPLA" http://www.cipher.
risk.tsukuba.ac.jp/tepla/index.html
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